The present application relates to a compact electromagnetic actuator capable of driving a lens assembly along X, Y, and Z axis.
With the continuous development of the mobile phone into a convergence device, more and more camera functions have been integrated into a mobile phone. Today, the voice coil motor (VCM) based autofocus camera function has been a standard feature of a high-end camera phone or a smart phone. Besides the autofocus (AF) function, the optical image stabilization (OIS) function is getting market interest and will soon become the next important camera feature to be integrated into the mobile phone. Various inventions about OIS have been disclosed, such as the ones in US patent applications of US2006/0061660, US2007/0103555, US2010/0098394, US2007/0236577, and US2013/0016428, and US patent of U.S. Pat. Nos. 7,881,598 and 7,725,014. Among all the disclosed inventions, three main types of technologies are mostly employed: (1) the body tilting method; (2) the body shifting method; and (3) the lens barrel tilting method.
Body Tilting Method (BTM)
Compared with the body shifting method (BSM), the BTM is based on tilting the AF camera module as a whole with respect to the optical axis to compensate for shaking or vibration. The key feature of this method is that a complete AF camera module is mounted on an image stabilization module or platform, wherein the AF camera module is installed with an imaging sensor, an imaging lens, and a lens actuator, and wherein the image stabilization module or platform is used to drive the complete AF camera module to tilt with respect to the optical axis. US2010/0098394 has disclosed an implementation based on the BTM. The problem of the BTM is its bulky size and its relatively higher power consumption than the BSM method as it drives the whole AF camera module. Obviously, the BTM method needs a large space for implementing the image stabilization module or platform.
Body Shifting Method (BSM)
This method is based on shifting/moving/swinging/displacing the autofocus actuator as a whole along the X and the Y directions. Therefore, a common feature of this method is that a complete AF actuator is mounted on an image stabilization module or platform, wherein the AF actuator is used to drive the lens holder (and hence the imaging lens assembly inside the holder) moving along the optical axis, and wherein the image stabilization module or platform is used to drive the complete AF actuator moving along the X and the Y directions in an XY plane perpendicular to the optical axis of the AF actuator. U.S. Pat. No. 7,881,598 and US2013/0016428 have respectively disclosed two electromagnetic actuators based on the BSM. Regardless of the details of the structure, a complete AF actuator is defined herein as a device which is configured to move a lens holder or an imaging lens assembly along an optical axis. Regardless of various terminologies used in all kinds of articles, patents, and patent applications, devices which satisfy the definition of AF actuator stated herein shall be considered as AF actuators as defined herein.
In the art, the BSM is also called as lens barrel shifting. Actually, it is not a real lens barrel shifting method as the lens barrel is not directly driven by the image stabilization module or platform. Lens barrel shifting is a result of the shifting of the AF actuator as a whole. The drawbacks of this method are its bulky size, large power consumption, slow response time, and etc. Having a bulky size is the most important problem among all the others. Because this method is based on shifting a complete AF actuator, the whole space needed must be larger than an AF actuator's size. This is a very natural and logical result. However, the current market situation is that customers' expectation on the size of the OIS actuator is exactly the same as the size of the AF actuator. Therefore, an actuator based on this method is hardly small enough or identical in size with the AF actuator. However, its advantage is that the image quality does not deteriorate with the shifting of the lens holder. At least, the image quality deterioration is not prominent.
Lens Barrel Tilting (LBT) Method
Compared with the BSM, the LBT method is based on tilting the lens barrel so that the lens assembly is tilted inside the lens holder to compensate for shaking or vibration. U.S. Pat. No. 7,725,014 has disclosed an actuator based on the LBT. The merit of the LBT method is that the image stabilization actuator directly drives the lens holder instead of driving the AF actuator. Since a lens holder is much lighter than a complete AF actuator, the OIS actuator based on the LBT method consumes less power than an OIS actuator based on the BSM. Moreover, due to the light weight of the lens holder, the response time of the LBT OIS actuator is also shorter than that of the BSM OIS actuator. Most importantly, the LBT OIS actuator can achieve the same size of the AF actuator as the AF function and the OIS function of the LBT actuator can be performed by the same set of actuators. Therefore, no extra space is needed. Furthermore, since both the AF and the OIS share the same set of actuators, not much extra material is needed for building the OIS actuator. It implies that such an OIS actuator is likely to have a low cost, at least comparable to the AF actuator's cost.
However, the problem of the LBT method is that the image quality deteriorates quickly as the tilting angle of the lens assembly increases. This significantly limits its applications. However, such problem does not occur to a BSM OIS actuator, or at least this problem is not prominent for the BSM OIS actuator.
In view of the above, there is a need to produce an electromagnetic actuator which is compact and low in power consumption and cost.
The above description of the background is provided to aid in understanding the compact electromagnetic actuator, but is not admitted to describe or constitute pertinent prior art to the compact electromagnetic actuator, or consider the cited documents as material to the patentability of the claims of the present application.